Flexible printed wiring boards comprising a circuit formed of a layer of a conductor such as a copper foil stacked on a flexible insulating film are known in the art.
With recent trends toward smaller electronic components, such flexible wiring boards involve connecting electrodes with finer pitches and an advanced multilayer structure.
This type of multilayer flexible wiring boards have typically been prepared by positioning each layer of wiring board to form a wiring pattern and bonding these layers into a multilayer structure.
With the prior art as described above, dimensional changes may vary between layers of wiring boards due to heat shrinkage during manufacturing processes or other factors, which means difficulty in stacking the wiring boards to electrically connect them.
Further, it is difficult to control dimensional changes in each layer of wiring board by this technique.
A film-like mask for exposure is sometimes used to form a circuit pattern in each layer of wiring board, which may add the influence of the shrinkage of the mask for exposure itself.
What is needed, therefore, is a process for manufacturing a multilayer flexible wiring board, which allows individual layers of wiring boards to be precisely positioned and to be readily stacked.